[Effect of shikonin and alkannin on hydroxyl radical generation system concerned with iron ion]

Inhibition of neutrophil superoxide generation by shikonin is associated with suppression of cellular Ca(2+) fluxes

Shikonin, an anti-inflammatory compound of “Shikon”, inhibits the neutrophil superoxide (O₂^•−) generation by NADPH oxidase 2 (Nox2); however, the mechanisms of how shikonin affects Nox2 activity remained unclear. We aimed to elucidate the relationship between the inhibition of Nox2 activity and influences on intracellular Ca²⁺ concentration ([Ca²⁺]_i) by shikonin. For this purpose, we used a simultaneous monitoring system for detecting changes in [Ca²⁺]_i (by fluorescence) and O₂^•− generation (by chemiluminescence) and evaluated the effects of shikonin on neutrophil-like HL-60 cells stimulated with N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLP). Since fMLP activates Nox2 by elevation in [Ca²⁺]_i via fluxes such as inositol 1,4,5-trisphosphate-induced Ca²⁺ release (IICR) and store-operated Ca²⁺ entry (SOCE), we also evaluated the effects of shikonin on IICR and SOCE. Shikonin dose-dependently inhibited the fMLP-induced elevation in [Ca²⁺]_i and O₂^•− generation (IC₅₀ values of 1.45 and 1.12 µM, respectively) in a synchronized manner. Analyses of specific Ca²⁺ fluxes showed that shikonin inhibits IICR and IICR-linked O₂^•− generation (IC₅₀ values: 0.28 and 0.31 µM for [Ca²⁺]_i and O₂^•−, respectively), as well as SOCE and SOCE-linked O₂^•− generation (IC₅₀ values: 0.39 and 0.25 µM for [Ca²⁺]_i and O₂^•−, respectively). These results suggested that shikonin inhibits the O₂^•− generation by Nox2 in fMLP-stimulated neutrophils by targeting Ca²⁺ fluxes such as IICR and SOCE.

Evaluation of radical scavenging properties of shikonin

With the aim of developing effective anti-inflammatory drugs, we have been investigating the biochemical effects of shikonin of “Shikon” roots, which is a naphthoquinone with anti-inflammatory and antioxidative properties. Shikonin scavenged reactive oxygen species like hydroxyl radical, superoxide anion (O₂^•−) and singlet oxygen in previous studies, but its reactivity with reactive oxygen species is not completely understood, and comparison with standard antioxidants is lacking. This study aimed elucidation of the reactivity of shikonin with nitric oxide radical and reactive oxygen species such as alkyl-oxy radical and O₂^•−. By using electron paramagnetic resonance spectrometry, shikonin was found unable of reacting with nitric oxide radical in a competition assay with oxyhemoglobin. However, shikonin scavenged alkyl-oxy radical from 2,2'-azobis(2-aminopropane) dihydrochloride with oxygen radical absorbance capacity, ORAC of 0.25 relative to Trolox, and showed a strong O₂^•−-scavenging ability (42-fold of Trolox; estimated reaction rate constant: 1.7 × 10⁵ M⁻¹s⁻¹) in electron paramagnetic resonance assays with CYPMPO as spin trap. Concerning another source of O₂^•−, the phagocyte NADPH oxidase (Nox2), shikonin inhibited the Nox2 activity by impairing catalysis when added before enzyme activation (IC₅₀: 1.1 µM; NADPH oxidation assay). However, shikonin did not affect the preactivated Nox2 activity, although having potential to scavenge produced O₂^•−. In conclusion, shikonin scavenged O₂^•− and alkyl-oxy radical, but not nitric oxide radical.

Antioxidant Activity of Anthocyanin Extract from Purple Black Rice

Antioxidant activity was studied for anthocyanins extracted from purple black rice (PBR) by a 3% aqueous trifluoroacetic acid solution (TFA), as well as for anthocyanins extracted from blueberry (Bluetta, high bush type). Capillary zone electrophoresis revealed that the PBR extract contained almost exclusively a single anthocyanin, which was identified as cyanidin 3-O-beta-D-glucoside (Cy 3-Glc) after purification by polyvinylpyrrolidone column chromatography. In contrast, 11 anthocyanins were identified in the blueberry extract. PBR extract showed slightly weaker superoxide scavenging and crocin bleaching activities than blueberry extract did. Both PBR and blueberry extracts, however, showed 10 to 25 times stronger activity than the same concentration of Trolox used as a reference antioxidant. It was further noted that the purified Cy 3-Glc from PBR extract retained approximately 74% of the antioxidant activity (both crocin bleaching and superoxide scavenging) observed in the original TFA extract. The hydroxyl radical scavenging activity of both extracts was several times weaker than that of the same concentration of Trolox, although the PBR extract showed approximately two times stronger activity than blueberry extract did. The hydroxyl radical scavenging activity of the purified Cy 3-Glc from PBR, however, decreased to approximately 20% of that of the original PBR extract. These results indicate that the anthocyanin Cy 3-Glc contributes to the antioxidant activity of PBR through its strong superoxide radical but not hydroxyl radical scavenging activity.

Antioxidant potential of qizhu tang, a chinese herbal medicine, and the effect on cerebral oxidative damage after ischemia reperfusion in rats

A traditional Chinese herbal medicine, Qizhu Tang (QZT) was studied for its in vitro antioxidant activity and the effect on cerebral oxidative damage after forebrain ischemia followed by reperfusion in rats. The QZT decoction was shown to have strong hydroxyl radical (*OH) scavenging activity (approx. 0.1 mM as Trolox equivalent) when determined by ESR using DMPO as a spin trap reagent and H2O2/UV as the *OH source. When the QZT decoction was injected into rat duodenum 2 h before cerebral ischemia, the oxidative brain damage after 45 min reperfusion was strongly inhibited in terms of two biochemical indications, thiobarbituric acid reactive substance formation and the loss of glutathione peroxidase. Since the QZT formula consists of 4 herbal constituents (Rhizoma atractylodis, Poria, Radix notoginseng and Radix astragali), each of the component herbs and their combinations were also examined for their protective effects on the cerebral ischemia/reperfusion injury and the effects were compared with their in vitro antioxidant potential. Although some of the incomplete formulas showed as strong antioxidant activities as complete QZT in vitro, only the complete QZT formula was effective in preventing cerebral oxidative injury in rats, and other preparations showed limited activity in vivo.

Reaction of beta-alkannin (shikonin) with reactive oxygen species: detection of beta-alkannin free radicals

beta-Alkannin (shikonin), a compound isolated from the root of Lithospermum erythrorhizon Siebold Zucc., has been used as a purple dye in ancient Japan and is known to exert an anti-inflammatory activity. This study aimed to understand the biological activity in terms of physico-chemical characteristics of beta-alkannin. Several physico-chemical properties including proton dissociation constants, half-wave potentials and molecular orbital energy of beta-alkannin were elucidated. This compound shows highly efficient antioxidative activities against several types of reactive oxygen species (ROS), such as singlet oxygen ((1)O2). superoxide anion radical (.O2), hydroxyl radical (.OH) and tert-butyl peroxyl radical (BuOO.) as well as iron-dependent microsomal lipid peroxidation. During the reactions of beta-alkannin with 1O2, .O2- and BuOO., intermediate organic radicals due to beta-alkannin were detectable by ESR spectrometry. Compared with the radicals due to naphthazarin, the structural skeleton of beta-alkannin, the beta-alkannin radical observed as an intermediate in the reactions with (1)O2, and .O2- was concluded to be a semiquinone radical. On the other hand, during the reactions of beta-alkannin and naphthazarin with BuOO., ESR spectra different from the semiquinone radical were observed, and proposed to result from the abstraction of hydrogen atoms from phenolic hydroxyl groups of beta-alkannin by BuOO.. Based on the ROS-scavenging abilities of beta-alkannin, the compound was concluded to react directly with ROS and exhibits antioxidative activity, which in turn exerts anti-inflammatory activity.